Light transmissive insulation apparatus

ABSTRACT

A light transmissive insulation system comprising a plurality of layers of light transmissive insulating material, the material being characterized by transmissivity to solar spectrum radiation, and low transmissivity to thermal radiation. A solar pond employing the insulation system is also described.

REFERENCE TO CO-PENDING APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 800,915 filed Nov. 25, 1985. U.S. patent application Ser. No.800,915 is a continuation of U.S. patent application Ser. No. 541,119filed Oct. 12, 1983 now abandoned. U.S. patent application Ser. No.541,119 is a continuation-in-part of U.S. patent application Ser. No.363,451, filed Mar. 30, 1982, now U.S. Pat. No. 4,480,632.

FIELD OF THE INVENTION

The present invention relates to insulation generally and moreparticularly to insulation apparatus and structures which aresubstantially light transmissive and are suitable for use with solarponds including defining portions of larger bodies such as lakes orseas.

BACKGROUND OF THE INVENTION

There is described and claimed in applicants' U.S. Pat. No. 4,480,632thermal insulation suitable for use along a solar radiation incidentsurface of a solar pond containing a pond liquid and including aplurality of transparent enclosures arranged to be disposed on a surfaceof a solar pond, at least one layer of insulative beads disposed withinthose enclosures, the layer of insulative beads defining a plurality ofbarrier layers separated from each other by insulating volumes definedby the insulating beads, a liquid material of viscosity greater than theviscosity of the pond liquid being arranged to fill the intersticesbetween the plurality of enclosures, the at least one layer ofinsulative beads definign the barrier layers being formed of a materialselected from the following materials: glass, fluoroplastics, acrylicsand polycarbonate and being characterized by transmissivity to solarradiation and opacity to thermal infro-red radiation in the wavelengthrange of 6-20 microns, the volumes defined by the insulative beads beingcharacterized by low thermal conductivity and high transparency to solarradiation.

There is described and claimed in co-pending U.S. patent applicationSer. No. 541,119 filed Oct. 12, 1983, solar radiation transmissiveinsulation apparaus comprising an array of adjacent cells having ageometrical configuration which limits free convection therethrough, thearray being generally transparent to solar visible and infra-redradiation and generally opaque to thermal infro-red radiation and asolar pond employing such insulation.

SUMMARY OF THE INVENTION

The present invention represents a further refinement and development ofthe insulation apparatus and system described and claimed in applicant'saforesaid U.S. Pat. No. 4,480,632 and co-pending application Ser. No.541,119.

In accordance with a preferred embodiment of the present invention,there is provided a solar pond comprising a body of material sought tobe heated, a layer of solar spectrum radiation transmissive insulationarranged to lie over the body of material and in spaced relationshiptherewith, the layer of solar spectrum radiation transmissive insulationcomprising an array of cells configured to minimize heat losses from thebody of material through convection and conduction, said array beinggenerally transmissive to solar spectrum radiation and generally opaqueto thermal radiation.

According to an embodiment of the present invention, the array of cellscomprises a plurality of elongated cells which when their longitudinalaxis is vertical, are square in plan and rectangular in section.

According to an alternative embodiment of the present invention thearray of cells comprises a plurality of elongated slanted cells.

According to an embodiment of the present invention, the pond materialsought to be heated comprises any material substantially absorbent ofsolar spectrum radiation such that a layer of that material typically upto one meter in thickness when exposed to solar spectrum radiation willbecome sufficiently heated such that energy is usable therefrom.

Pond materials may comprise any appropriate organic or inorganicmaterial or a suitable combination thereof.

Also according to the above embodiment of the present invention, thepond material may comprise at least two mutually immiscible materialscomprising distinct layers wherein these layers may comprise a solid ora liquid.

It is also a feature of this embodiment of the invention that theuppermost layer may have a lower vapour pressure than any layerstherebelow, in order substantially to prevent thermal energy loss byevaporation of the lower layers through the uppermost layer.

Examples of liquids that are suitable for use as an upper layer in theabove-described embodiment of the invention wherein the lower layersubstantially comprises water are film forming materials such as oil orcetyl alcohol.

It should be noted that in all preferred embodiments of the presentinvention the pond material comprises a liquid.

According to one embodiment of the invention, the solar spectrumradiation transmissive insulation is mounted on a fixed support securedto the floor of the body of liquid. According to an alternativeembodiment of the invention, the solar spectrum radiation transmissiveinsulation is mounted on buoys floating on the body of liquid. Accordingto a further alternative embodiment of the invention, the solar spectrumradiation transmissive insulation is mounted on elongate tubes floatingon the body of liquid.

In accordance with one preferred embodiment of the invention, the solarspectrum radiation transmissive insulation is provided with a generallytilted top surface to provide rain runoff therefrom.

Additionally in accordance with an embodiment of the present inventionthere is provided a solar pond comprising a body of material sought tobe heated, a layer of solar spectrum radiation transmissive insulationarranged to lie over the body of material, the layer of solar spectrumradiation transmissive insulation comprising an array of cellsconfigured to minimize heat losses from the body of liquid throughconvection and conduction, said array being generally transmissive tosolar spectrum radiation and generally opaque to thermal radiation, thearray being surrounded by a generally sealed enclosure comprising planarglass panels defining top, bottom and side surfaces and being joined bysealing means, venting apparatus being provided for permittingcommunication between the interior and exterior of the enclosure.

According to an embodiment of the present invention, the array of cellscomprises a plurality of elongated cells which when their longitudinalaxis is vertical, are square in plan and rectangular in section.

According to an alternative embodiment of the present invention thearray of cells comprises a plurality of elongated cells, which whentheir longitudinal axis is vertical, are square in plan and rhomboid insection.

As noted above, although pond materials may comprise any appropriateorganic or inorganic material or any suitable combination thereof, inpreferred embodiments of the present invention the pond materialcomprises a liquid.

In the above embodiment, the solar radiation transmissive insulation maybe arranged in spaced relationship above the body of liquid oralternatively floating directly on the top surface of the body ofliquid.

In one embodiment of the invention there are provided downwardlyextending peripheral surfaces arranged to form a skirt below theenclosure whereby an air gap is defined by the bottom of the enclosure,the body of liquid and the skirt. In this embodiment there may also beprovided means for the provision of air to the air gap for theregulation thereof.

In an alternative embodiment the enclosure is floating on the body ofliquid and its bottom surface is preferably blackened.

Additionally in accordance with an embodiment of the invention, there isprovided for use in a solar pond, comprising a body of material soughtto be heated, a layer of solar spectrum radiation transmissiveinsulation arranged to lie over the body of material and in spacedrelationship therewith, the layer of solar spectrum radiationtransmissive insulation comprising an array of cells configured tominimize heat losses from the body of material through convection andconduction, said array being generally transmissive to solar spectrumradiation and generally opaque to thermal radiation.

According to an embodiment of the present invention, the array of cellscomprises a plurality of elongated cells which when their longitudinalaxis is vertical, are square in plan and rectangular in section.

According to an alternative embodiment of the present invention thearray of cells comprises a plurality of elongated cells, which whentheir longitudinal axis is vertical, are square in plan and rhomboid insection.

As noted above, although pond materials may comprise any appropriateorganic or inorganic material or any suitable combination thereof, inpreferred embodiments of the present invention the pond materialcomprises a liquid.

According to one embodiment of the invention, the solar spectrumradiation transmissive insulation is mounted on a fixed support securedto the floor of the body of liquid. According to an alternativeembodiment of the invention, the solar spectrum radiation transmissiveinsulation is mounted on buoys floating on the body of liquid. Accordingto a further alternative embodiment of the invention, the solar spectrumradiation transmissive insulation is mounted on elongate tubes floatingon the body of liquid.

In accordance with one preferred embodiment of the invention, the solarspectrum radiation transmissive insulation is provided with a generallytilted top surface to provide rain runoff therefrom.

Additionally in accordance with an embodiment of the present inventionthere is provided for use in a solar pond comprising a body of materialsought to be heated, a layer of solar spectrum radiation transmissiveinsulation arranged to lie over the body of material, the layer of solarspectrum radiation transmissive insulation comprising an array of cellsconfigured to minimize heat losses from the body of material throughconvection and conduction, said array being generally transmissive tosolar spectrum radiation and generally opaque to thermal radiation, thearray being surrounded by a generally sealed enclosure comprising planarglass panels defining top, bottom and side surfaces and being joined bysealed means, venting apparatus being provided for permittingcommunication between the interior and exterior of the enclosure.

According to an embodiment of the present invention, the array of cellscomprises a plurality of elongated cells which when their longitudinalaxis is vertical, are square in plan and rectangular in section.

According to an alternative embodiment of the present invention thearray of cells comprises a plurality of elongated cells, which whentheir longitudinal axis is vertical, are square in plan and rhomboid insection.

As noted above, although pond materials may comprise any appropriateorganic or inorganic material or any suitable combination thereof, inpreferred embodiments of the present invention the pond materialcomprises a liquid.

According to the above embodiment, the solar spectrum radiationtransmissive insulation may be arranged in spaced relationship above thebody of liquid or alternatively directly floating on the top surface ofthe body of liquid.

In an additional embodiment of the invention there are provideddownwardly extending peripheral surfaces arranged to form a skirt belowthe enclosure whereby an air gap is defined by the bottom of theenclosure, the body of liquid and the skirt. In this embodiment theremay also be provided means for the provision of air to the air gap forthe regulation thereof.

In an alternative embodiment the enclosure is floating on the body ofliquid and its bottom surface is preferably blackened.

Apparatus for heat extraction and energy conversion may, of course, beprovided in combination with the above-described apparatus in accordancewith a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description, taken in conjunction with thedrawings in which:

FIG. 1 is a sectional illustration of a solar pond covered withinsulative rafts constructed and operative in accordance with analternative embodiment of the present invention;

FIG. 2 is a pictorial illustration of solar radiation transmissivethermal insulation material constructed and operative in accordance witha preferred embodiment of the present invention;

FIGS. 3 and 4 are sectional illustrations of two alternative embodimentsof solar radiation transmissive thermal insulation material constructedand operative in accordance with a preferred embodiment of the presentinvention;

FIGS. 5A, 5B, and 5C are respective plan, sectional and side viewillustrations of solar radiation transmissive thermal insulationmaterial constructed and operative in accordance with an alternativeembodiment of the present invention;

FIG. 6 is a pictorial illustration of a solar radiation transmissivethermal insulation module forming part of a solar pond in accordancewith one embodiment of the present invention;

FIG. 7 is a side view, sectional illustration of a raft enclosure usefulin the embodiment of FIG. 6;

FIG. 8 is a sectional illustration of an assembled raft according to analternative embodiment of the present invention;

FIG. 9 is a pictorial illustration of the insulative material used inthe embodiment of FIGS. 7 and 8 and illustrating a portion of thetechnique for manufacturing same;

FIG. 10 is a pictorial illustration of an insulation module constructedand operative in accordance with a preferred embodiment of the presentinvention;

FIGS. 11A, 11B and 11C are enlarged illustrations of portions of theinsulation module of FIG. 10;

FIG. 12A is a top view illustration of a fixed mounting structuredesigned and operative in accordance with an embodiment of the presentinvention;

FIG. 12B is a side view illustration of insulation modules, mounted onthe mounting structure of FIG. 12A;

FIG. 12C is a side view illustration of insulation modules mounted on analternative embodiment of the mounting structure of FIG. 12A;

FIG. 13A is a top view illustration of a floating mounting structurefloating on buoys designed and operative in accordance with anembodiment of the present invention;

FIG. 13B is a side view illustration of insulation modules, mounted onthe floating mounting structure of FIG. 13A;

FIG. 13C is a side view illustration of insulation modules mounted on analternative embodiment of the mounting structure of FIG. 13A;

FIG. 13D is a side view illustration of insulation modules mounted onthe floating mounting structure of FIG. 13B but where the pond materialcomprises of two mutually immiscible liquids;

FIGS. 14A and 14B are respective top and side view illustrations ofinsulation modules mounted on floating tubular structures;

FIG. 15A is a pictorial illustration of an insulation module constructedand operative in accordance with an alternative preferred embodiment ofthe present invention;

FIG. 15B is an enlarged illustration of part of the module of FIG. 15A;

FIG. 15C is a side view illustration of the operation of the insulationmodules of FIG. 15A; and

FIG. 16 is a pictorial illustration of an insulation module constructedand operative in accordance with a further preferred embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference is now made to FIG. 1 which illustrates a solar pondconstructed and operative in accordance with a preferred embodiment ofthe present invention. The solar pond comprises a pond liner 10 whichencloses the pond from the bottom and sides and is peripherally anchoredin the surrounding earth by an anchor 12. A peripheral thermalinsulating side surface layer 14 is provided adjacent the top surface ofthe pond as illustrated.

The solar pond comprises typically non-saline water and its surface iscovered with an array of modular insulating raft assemblies 16, theconstruction of which will be described in detail hereinafter. It is aparticular feature of the present invention that the pond can employ anytype of water or other fluid. A heater water outlet conduit 18communicates with the interior of the pond near its top surface forremoving heated water therefrom for external use. A return water supplyconduit 20 typically communicates with the interior of the pond at aslightly lower level.

According to a preferred embodiment of the present invention, mixermeans 22, typically in the form of one or more rotating impellers orsuitably directed water jets, are provided in the pond for providing agenerally homogeneous temperature layer of water at high temperatureadjacent the surface of the pond. This layer is relatively stableagainst heat losses due to convection from adjacent layers of waterlying therebelow.

Reference in now made to FIG. 7 which illustrates the construction ofraft assemblies 16. Raft assemblies 16 comprise a molded bottom assembly24, which is typically formed of G.M.T., continuous glass fibrereinforced plastic such as Polypropylene, and has a generallyrectangular configuration. The bottom assembly typically includes abottom recess 26 which accomodates a weight 28 for providing raftstabilization. Extending upwardly and outwardly of the bottom recess isan inclined bottom wall 30 which terminates in peripheral side walls 32.Formed on side walls 32 is a peripheral lid support protrusion 34. It isnoted that the bottom assembly, when fully assembled as part of the raftis designed to ride in the water such that the water line is locatedapproximately at the bottom of the side walls 32, such that theinsulating material located within the bottom assembly liessubstantially above the water surface.

A lid member 36 is assembled onto the side wall 32 of the bottomassembly. The lid member 36 is formed with an inclined top surface 38 toprovide drainage of rainwater and with a peripheral engagement clipconfiguration 40 which provides positive sealed engagement with the topof side walls 32 of the bottom assembly. The positive sealed engagementmay be provided by a labyrinth seal configuration molded into theperipheral walls defining clip configuration 40 and/or into side walls32. A bottom surface 42 is arranged to abut against protrusion 34 ofside walls 32.

The lid member 36 is preferably formed of PMMA (PolyMethylMethacrylate),UV protected polycarbonate or glass by injection molding themoforming,or any other suitable technique. It is preferably characterized in thatit is transparent to radiation in the solar spectrum. Preferably it hasa low refractive index or is surface treated by conventional techniquesto reduce reflectivity. It is preferably opaque to thermal infra-redradiation and displays high durability when exposed to sunlight andhumidity.

As seen in FIG. 7, each of adjacent raft assemblies 16, containsinsulation apparatus 50 of the type illustrated typically in FIG. 2 anddescribed hereinbelow. A layer of a refluxing fluid, such as lowmolecular weight silicone oil may be provided within the sealedenclosures defined by raft assemblies 16, for coating the surfaces ofthe raft assemblies and of the insulating apparatus by refluxing toprevent surface deterioration of the surfaces which results in haze andconsequent enery losses.

A layer 52 of oil, such as ordinary light machine oil, is locatedintermediate adjacent rafts and not therebeneath, in order to preventevaporation of the interstices between adjacent rafts.

Reference is now made to FIG. 2 which illustrates a solar energytransmissive thermal insulation material constructed and operative inaccordance with a preferred embodiment of the present invention. Theoverall characteristics of the material are as follows:

1. Minimal absorption (i.e. less than about 20%) in the range of solarradiation, i.e. from approximately 0.3 to 2.0 microns.

2. High absorption (i.e. at least about 80%) in the range of thermalinfra-red radiation, i.e. between approximately 6 to 25 microns.

3. Minimal reflectivity (i.e. less than approximately 20%) to incidentdiffuse radiation within the solar spectrum.

4. Low thermal convection and conduction heat losses (in the range ofapproximately 0.1-0.2 Watt/meter degree Centigrade or less).

According to a preferred embodiment of the present invention, the solarradiation transmissive thermal insulation material comprises an array110 of cells 112 having a geometrical configuration which is selected tominimize both convection and conduction thermal losses. Within thecontext of a cell having a uniform cross sectional configuration, thegeometrical configuration which minimizes conduction and convection maybe appreciated to have an aspect ratio which is maximized against across sectional circumference which is minimized. The aspect ratio isdefined as the ratio between the length (height) of the cell and itscharacteristic hydrodynamic cross sectional diameter. Thischaracteristic hydrodynamic cross sectional diameter is a well knowndefined quantity for all common types of geometrical cross sectionalshapes, such as squares, triangles, etc., and is equal to4(area)/circumference.

According to a preferred embodiment of the present invention, crosssectional configurations having a high ratio of area to maximumseparation between adjacent side walls are employed. Thus circular,hexagonal, triangular, and square cross sectional configurations arepreferred over rectangular and other configurations, even though suchconfigurations may be used nevertheless for reasons related to ease andeconomy of manufacture.

According to a preferred embodiment of the present invention, an aspectratio of between 5 and 50 is preferred. The maximum separation betweenadjacent side walls is selected to minimize free convection through thecell under the temperature gradient conditions encountered duringoperation. The relationship between temperature gradient and the desiredmaximum separation between adjacent side walls for substantialprevention of free convection is described in Heat Transmission, byWalter N. McAdams, 3rd edition, McGraw Hill Book Company, at pages170-182, especially pages 181-182.

In the present invention, the operational temperature gradientsparticularly for solar pond applications are expected to be in the rangeof 2-15 degrees centigrade/cm and thus the maximum separation betweenside walls of the cells is selected to be about 1 cm or less in order tolimit the free convection losses to less than 1 Watt / square meterdegree Centigrade.

It is appreciated that there exists a certain trade off in thedetermination of the thickness of the side walls of the cells 112 sincethe greater the wall thickness, the greater is the absorption of thermalinfra-red radiation and the smaller the wall thickness, the smaller isthe thermal conduction produced by the side walls. Accordingly, thethickness of the side walls is determined in order to minimize theoverall energy losses due to back radiation in the thermal infra-redrange and conduction through the cell walls. In the illustratedembodiment, a side wall thickness of approximately 10-50 microns ispreferred on the basis of projections made by the inventors herein.

In the illustrated embodiment of the present invention, polycarbonateplastic is currently considered to be the best available material from acost effectiveness standpoint. It is appreciated that other types ofplastic materials such as polymethacrylates (perspex), thermoplasticpolyesters, fluorocarbons (PVF, FEP, etc) in combination withappropriate additives, and polyacrylate or glass may also be used.

It is appreciated that the provision of a particularly smooth side wallsurface for the cells is particularly important to maintain their solarradiation transmission efficiency. Since it is known that plasticsurfaces tend to dry out over time as the result of prolonged exposureto intensive solar radiation and their surface tends to become cloudy,it is proposed to provide a small quantity of liquid within each cell.The liquid undergoes a continuous cycle of evaporation and condensationalong the vertical temperature gradient and thus coats the side walls ofthe cells with a liquid coating preventing clouding thereof.

FIG. 3 illustrates a configuration of a cell array which is believed tobe particularly easy and convenient to manufacture. FIG. 3 is a topsectional view and indicates that the individual cells are defined bythe junctions between alternating flat and corrugated layers of plasticwhich are joined at their junctions to define the individual cells.

FIG. 4 illustrates an alternative configuration of a cell array which ismade up of a multiplicity of tubes joined together in parallelorientation to define individual cells. FIGS. 5A, 5B, and 5C illustratea further alternative configuration of a cell array which is comprisedof a pair of nested surfaces of egg carton type configuration, each ofwhich defines an array of spaced finger portions 117 which define thecells. The finger portions 117 of one such surface facing in a firstdirection are interdigitated with the finger portions 117 of a secondsuch surface facing in an opposite direction whereby the finger portions117 of one surface lie in the interstices between the finger portions117 of the other surface.

Reference is now made to FIG. 6 which illustrates a solar energytransmissive thermal insulating module 120 forming part of a solar pondconstructed and operative in accordance with an embodiment of thepresent invention. The module 120 comprises an array 122 of the typeillustrated in any of FIGS. 2-5C having sealed thereto top and bottomplates 124 and 126 to define a sealed unit which is adapted to float onthe top surface of a body of water or to be seated on any other desiredsurface.

When module 120 forms part of an insulating top layer of a solar pond,it is a particular feature of the pond that the module in naturallyoriented in a plane which lies tangent to the earth's surface at thatlocation. Thus a maximal orientation of the cells with respect to thesum is provided.

Bottom plate 126 of module 120 may either comprise a transparent plateformed of the same material as the remainder of the module and the arrayor alternatively may comprise a solar energy absorbing plate and may becolored black accordingly. Top plate 124 is formed of a glazing materialsuch as transparent plastic material which is preferably the samematerial as is used for the array 122.

It may be appreciated that the module of FIG. 6 has the followingproperties:

1. It is substantially transparent to solar radiation.

2. It is generally opaque to back radiation from the covered body ofwater in the infra-red band in the range of 6-20 microns.

3. It is generally resistant to liquid leakage and molecular diffusiontherethrough.

According to a preferred embodiment of the present invention, a highlyviscous liquid material may be provided on the surface of the solar pondin the interstices between the rafts. This liquid material layerprovides damping of the motion of the rafts and also provides a vapordiffusion barrier at the interstices. Preferably the material should betranslucent. A suitable mateial is polymethyl siloxane having aviscosity 10³ -10⁴ centistokes, low volatility and density less thanunity.

Reference is now made briefly to FIG. 8, which illustrates analternative preferred embodiment of the invention in which the module120 is mounted on a plurality of sealed heat conductive tubes or otherprofiles 140, which provide buoyancy, while maintaining good thermalcoupling between the module 120 and the underlying water. Profiles 140are typically formed of aluminum or any other suitable corrosionresistant thermal conductor.

The structure of FIG. 8 is particularly suitable for pond constructionswherein ease of interconnection and stability of rafts is desired.

Reference is now made to FIG. 9 which illustrates a technique formanufacture of the insulation apparatus of FIG. 2. As a first step, amultiple sheet hollow profile 190 is produced by extrusion frompolycarbonate or other suitable material and cut into long slabs.

The slabs are then stacked and slightly pressed together to ensurecontact between walls of adjacent slabs. A hot, thin metal wire 192, orseries of such wires, is then driven through the stacked profiles in adirection 194 perpendicular to the direction 193 of extrusion and isoperative to melt the plastic material at the contact surface with thefollowing effects:

a. cutting through the stacks longitudinally along axis 194.

b. welding the adjacent edges of adjacent slabs together.

The cutting and welding steps may alternatively by performed by asuitable laser beam.

The result is a slice formed of a plurality of joined slabs, which sliceis located within the sealed raft as described hereinabove.

The basic characteristics of the assembled raft assembly including theinsulation aparatus are as follows:

Thermal stability up to about 100 degrees centigrade.

Mechanical and dimensional stabiility against accumulative shearingforces caused by wind up top 40 m/sec at 100 m fetch.

Floating stability notwithstanding waves, inhibition of waves or theirformation.

Extremely low transmissivity of water vapor by diffusion in order toavoid interior accumulation of water by condensation.

The optical and other characteristics are already described hereinabovein connection with the description of the insulation material.

Reference is now made to FIGS. 10 and 11A in which are shown aninsulation module 200, constructed according to a preferred embodimentof the present invention. The module 200 comprises a top planarrectangular surface 202, parallel to a similar bottom surface 203,rectangular side walls 204 which typically are mutually parallel andperpendicular to and disposed between the above-mentioned top and bottomsurfaces and a pair of similar side walls 206, disposed bewteen andperpendicular to side walls 204.

In order to provide a water-tight seal to the module there is provided asealing strip 208 located along all of its edges. Incorporated intosealing strip 208 are a plurality of vents 210.

Each vent 210, as shown in FIG. 11a is tube-like in section having acontinuous passage 211, formed to have an exit 213 which is spaced abovetop surface 202 and exits into the atmosphere in a generally downwarddirection, so as to prevent the intrusion of rain water into module 200.

The function of vents 210 is to prevent the formation of high positiveor negative pressures within module 200. If such pressures were allowedto build up, they would create conditions of fatigue within the modulematerial within an unacceptably short period of time and wouldeventually lead to material failure and inefficient functioning of themodule and the possible drawing inward of water from outside module 200.

It will be appreciated that module 200 has the following properties:

1. it is substantially transparent to solar radiation;

2. it is generally opaque to back radiation from the covered body ofwater in the infra-red band of 6-20 microns; and

3. it has additional properties as listed hereinabove with reference toFIG. 6.

Reference is now made additionally to FIGS. 11B and 11C in which areshown enlarged views of the internal structure of insulation module 200.Shown in FIG. 11B and 11C is an array of cells 212. Each such cell is,as shown, typically square in plan and rectangular in section, typicaldimensions being 4 mm×4 mm×100 mm. The manufacturing process forobtaining cell array 212 is substantially as described hereinabove withreference to FIG. 9.

In FIGS. 12A and 12B there is shown an embodiment of the presentinvention wherein a metal framework 214 is attached to substantiallyvertical fixed legs 216 which are further supported by foundation slabs218, typically as shown. The frame work 214 and legs 216 may be of anysuitable construction and material but are preferably made from analuminum alloy which has suitable properties of strength, lightness,ductility and high resistance to corrosion.

An array 220 of insulation modules 200 (FIG. 10) is located on thesupporting framework 214 with suitable sealing strips 215 locatedbetween modules.

Array 220 is located above the water level indicated by referencenumeral 222 such that an air gap 224 is created between the array 220and the water level 222.

The presence of air gap 224 serves to prevent scale on the bottomsurface 226 of the array 220 which would otherwise occur were array 220in contact with water. Hence air gap 224 maintains transparency of array220 and in so doing ensures continued and efficient penetration of solarradiation to a depth typically of 1m in clear water. Air gap 224 servesadditionally to insulate the body of liquid contained within the solarpond against heat losses.

It is desirable in accordance with an embodiment of the presentinvention to tint the water. The presence of a coloring agent in thewater serves to regulate the depth of penetration of solar radiation andalso to limit reflection of solar radiation off the water surface 222.

Also shown is an optionally provided incline of array 220 as indicatedby reference numeral 228, typically in the order of 1%-2%. The provisionof such an incline ensures the runoff of rain water and helps to preventits uncontrolled incursion into the solar pond.

Shown additionally in FIG. 12C is an alternative array 221 of insulationmodules 200 (FIG. 10). Array 221 is indirectly located on supportingframework 214, being attached thereto by channel structure 217 and beingsupported on the edges thereof. Channel 217, serves to provideinter-module drainage, draining away any runoff that may be caused byrain.

In FIGS. 13A and 13B there is shown an embodiment of the presentinvention wherein a metal framework 234 is attached to and supported byfloating byoys 238. Framework 234 may be attached directly to buoys 238or indirectly thereto by short substantially vertical legs 236.

An array 240 of insulation modules 200 is disposed on the supportingframework 234 with suitable sealing strips 235 located between modules.

Array 240 is located above the water level 242 such that an air gap 244is created between the array 240 and the water level 242.

It should be noted that the function of air gap 244 is generally similarto that of air gap 224 as described with reference to the embodiment ofFIGS. 12A and 12B. Additionally, it is desirable to tint the water, asdescribed also with reference to the embodiment of FIGS. 12A and 12B.

Also shown in FIG. 13B is an optionally provided incline of array 240 asindicated by reference numeral 248 and whose function is similar to thatof the incline described with reference to the embodiment of FIGS. 12Aand 12B.

Shown additionally in FIG. 13C is an alternative array 241 of insulationmodules 200 (FIG. 10). Array 241 is indirectly located on supportingframework 234, being attached thereto by channel structure 237 and beingsupported on the edges thereof. Channel 237 serves to provideinter-module drainage, draining away any runoff that may be caused byrain.

In FIG. 13D there is shown an alternative embodiment of the presentinvention. Above water level 242 there is shown an additional layer 234which is immiscible with water and the vapour pressure of which is lowerthan that of water. In accordance with an embodiment of the invention,layer 243 comprises a film forming material, typically, oil or cetylalcohol.

In FIGS. 14A and 14B there is shown an embodiment of the presentinvention wherein a sealed and substantially hollow framework 254 whichis preferably tubular and formed of metal, floats directly on watersurface 262. Framework 254 may additionally comprise a small drainagechannel 256 upon the edge of which are located insulation modules 200(FIG. 10) which make up an array 260 of such modules.

According to another embodiment, there is provided an array ofinsulation modules 260 disposed on the supporting framework 254 withsuitable sealing strips located between modules 200.

Additionally, it is noted that array 260 is located above the waterlevel 262 such that an air gap 264 is created between the array 260 andthe water level 262.

It should be noted that the function of air gap 264 is generally similarto that of air gap 224 as described with reference to the embodiment ofFIGS. 12A and 12B. Additionally, it is desirable to tint the water, asdescribed also with reference to the embodiment of FIGS. 12A and 12B.

Also shown in FIG. 14B is an optionally provided incline of array 260 asindicated by reference numeral 268 and whose function is similar to thatof the incline described with reference to the embodiment of FIGS. 12Aand 12B.

With reference to FIG. 15A and 15B there is shown an insulation module300 constructed according to an additional embodiment of the presentinvention. Module 300 is substantially the same as that shown anddescribed with reference to FIGS. 10 and 11A and has similarcharacteristics and properties, except that in the present embodiment ofthe invention there are provided downwardly extending peripheralsurfaces arranged to form a skirt shown by numeral 312 which extendsbelow the enclosure whereby an air gap is defined by the bottom of theenclosure referenced 306, the body of liquid and the skirt 312.

With reference being made additionally to FIG. 15C, insulation modules300 are located on body of liquid 310. Skirt 312 extends into the waterto a point just below water surface 314 such that an air pocket 316 isformed between enclosure bottom surface 306 and water surface 314.

It should be noted that the function of air pocket 316 is generallysimilar to that of air gap 224 as described with reference to theembodiment of FIGS. 12A and 12B. Additionally, it is desirable to tintthe water, as described also with reference to the embodiment of FIGS.12A and 12B.

Indicated by reference numeral 318 there is additionally shown apparatusfor the provision of air to air pockets 316 for the regulation thereof.Apparatus 318 may comprise any suitable air pump or other air provisionmeans.

Shown in FIG. 16 is an insulation module indicated by numeral 400,designed and constructed in accordance with an additional embodiment ofthe present invention. There was shown in FIGS. 10, 11A, 11B and 11C aninsulation moduel 200, the internal structure of which comprises anarray of cells 212 substantially vertical in section. Insulation module400 comprises an internal structure comprising an array of cells 412,which are diagonal in section.

A measure of the efficiency of the insulation apparatus of the presentinvention may be made by comparison of the longitudinal axis througheach of the cells comprised in array 412 with an angle of incidence ofthe sun. When the angle of incidence of the sun is coincident with thatof the longitudinal axis of cells constituting array 412 then there is aminimum of diffusion of the sun's rays and more solar energy reaches thebody of liquid in the provided solar pond.

In regions where the maximum angle of incidence of the sun issignificantly below 90 degrees, the insulation apparatus embodied in thepresent invention will have increased efficiency if an angled array 412is used.

It should be noted that all other characteristics of module 400 aresubstantially the same as those described hereinabove with regard toFIGS. 10, 11A, 11B and 11C, and that it may be used in any of thepreferred embodiments of the present invention hereinabove described.

It should additionally be noted that techniques for manufacture of array412 are substantially the same as those hereinabove described withreference to FIG. 9, except that in order to obtain an array of slantedcells, the described stacked slabs are cut at a preselected angle andnot as described therein.

It will be appreciated by persons skilled in the art that the inventionis not limited by what has been particularly shown and describedhereinabove. Rather the scope of the present invention is defined onlyby the claims which follow.

We claim:
 1. A solar pond comprising a body of liquid material sought tobe heated, a layer of solar spectrum radiation transmissive insulationarranged to lie over said body of liquid material in a non-contactspaced relationship therwith so as to form an air gap therebetween,wherein said layer of solar spectrum radiation transmissive insulationcomprises an array of cells generally transmissive to solar spectrumradiation and generally opaque to thermal radiation, the array beingsurrounded by a generally sealed enclosure comprising planar glasspanels defining top, bottom and side surfaces and being joined bysealing means, said enclosure including venting apparatus for permittingcommunication between the interior and exterior of the enclosure, eachof said cells in said array having a uniform non-rectangular planarcross section and an aspect ratio which is selected from a range between5 and 50 to minimize free convection therethrough, the insulationapparatus being configured such that only a single layer of cells isdisposed between the liquid material sought to be heated and the sun,said non-contact spaced relationship being provided by a fixed supportsecured to the bottom of said solar pond for mounting said solarradiation transmissive insulation thereon, said air gap minimizing scalebuildup on said enclosure bottom surface and providing insulationagainst heat loss from the pond.
 2. A solar pond according to claim 1wherein said array of cells comprises a plurality of elongated slantedcells.